Transmtting ppdu

ABSTRACT

A method for transmitting a physical layer protocol data unit (PPDU) and a device using the same are provided. The device receives a trigger frame for requesting a transmission of a response PPDU and transmits the response PPDU. A duration of the response PPDU is calculated based on a duration of the trigger frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/821,639 and claims the benefit of priority of Korean PatentApplication Nos. 10-2016-0155495 filed on Nov. 22, 2016, 10-2016-0157322filed on Nov. 24, 2016, 10-2016-0165637 filed on Dec. 7, 2016, and10-2016-0168422 filed on Dec. 12, 2016, all of which are incorporated byreference in their entirety herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communication and, moreparticularly, to a method and device for transmitting a data unit in awireless local area network.

Related Art

Institute of Electrical and Electronics Engineers (IEEE) 802.11 basedwireless local area networks (WLANs), the most popular and successfulindoor wireless solutions, have evolved as a key enabling technology tocover medium to large scale enterprises, public area hot-spots,apartment complexes, and are ubiquitous in the modern world.

High Efficiency (HE) WLAN (e.g., IEEE 802.11ax) improves a spectrumefficiency and an area throughput in a dense environment. Especially, inan indoor or an outdoor environment, a purpose of the HE WLAN is toimprove a performance when a lot of access points (APs) and stations(STAs) are competing.

Since a lot of APs and STAs are competing, an improved protectionmechanism to prevent a collision due to simultaneous transmissions ofSTAs is required.

SUMMARY OF THE INVENTION

The present invention provides a method and device for transmitting aphysical layer protocol data unit (PPDU) in a wireless local areanetwork is provided.

In an aspect, the method includes receiving a trigger frame forrequesting a transmission of a response PPDU, the trigger frame includesa first duration field, a length field and a resource allocation field,the resource allocation field indicating a resource allocated to thetransmission of the response PPDU, and transmitting the response PPDU asa response to the trigger frame. The response PPDU includes a secondduration field, the second duration field being set to a value obtainedby D1-D2. D1 is a value obtained from the first duration field of thetrigger frame. D2 is a value obtained by:

${SIFS} + {\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension}$

where Short Interframe Space (SIFS) is 10 microseconds (ps) or 16 μs,LENGTH is a value of the length field in the trigger frame andSignalExtension is 0 μs or 6 μs.

In another aspect, a device includes a transceiver configured to receiveand transmit radio signals, and a processor coupled with thetransceiver. The processor is configured to control the transceiver toreceive a trigger frame for requesting a transmission of a responsePPDU, the trigger frame includes a first duration field, a length fieldand a resource allocation field, the resource allocation fieldindicating a resource allocated to the transmission of the responsePPDU, and control the transceiver to transmit the response PPDU as aresponse to the trigger frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows various formats for HE PPDU.

FIG. 2 shows a boundary of a PPDU.

FIG. 3 shows the difference of RXTIME between HE STA and legacy STA.FIG.

FIG. 4 shows the NAV procedure of HE STA after receiving HE PPDU.

FIG. 5 shows an example of uplink multi-user operation.

FIG. 6 shows a format of Trigger frame.

FIG. 7 shows a protection when HE TB PPDU is transmitted.

FIG. 8 shows an example of MU UL transmission.

FIG. 9 shows the NAV procedure of HE STA after receiving HE TB PPDU.

FIG. 10 shows an example of the Duration field in the HE TB PPDU.

FIG. 11 shows an example of the Duration field in the HE SU PPDU, HE ERSU PPDU and HE MU PPDU.

FIG. 12 shows an example of the Duration field in the HE TB PPDU.

FIG. 13 shows an example of the Duration field in the HE SU PPDU, HE ERSU PPDU and HE MU PPDU.

FIG. 14 shows a block diagram of a device to implement embodiments ofthe present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The proposed wireless local area network (WLAN) system may operate at aband less than or equal to 6 GHz or at a band of 60 GHz. The operatingband less than or equal to 6 GHz may include at least one of 2.4 GHz and5 GHz.

For clarity, a system complying with the Institute of Electrical andElectronics Engineers (IEEE) 802.11 a/g standard is referred to as anon-High Throughput (non-HT) system, a system complying with the IEEE802.11n standard is referred to as a High Throughput (HT) system, and asystem complying with IEEE 802.11ac standard is referred to as a VeryHigh Throughput (VHT) system. In comparison thereto, a WLAN systemcomplying with the proposed method is referred to as a High Efficiency(HE) system. A WLAN system supporting systems used before the HE systemis released is referred to as a legacy system. The HE system may includean HE Station (STA) and an HE Access Point (AP). The term HE is only forthe purpose of distinguishing from the conventional WLAN, and there isno restriction thereon. The HE system may support IEEE 802.11/a/g/n/acby providing backward compatibility in addition to the proposed method.

Unless a function of a station (STA) is additionally distinguished froma function of an Access Point (AP), the STA may include a non-AP STAand/or the AP. When it is described as an STA-to-AP communication, theSTA may be expressed as the non-AP STA, and may correspond tocommunication between the non-AP STA and the AP. When it is described asSTA-to-STA communication or when a function of the AP is notadditionally required, the STA may be the non-AP STA or the AP.

A Physical layer Protocol Data unit (PPDU) is a data unit for datatransmission. A basic service set (BSS) may include a set of STAs thathave successfully synchronized with an AP. A basic service setidentifier (BSSID) is a 48 bits identifier of a corresponding BSS. Anoverlapping basic service set (OBSS) may be a BSS operating on the samechannel as the STA's BSS. The OBSS is one example of different BSS withthe STA's BSS.

Enhanced Distributed Channel Access (EDCA) channel access protocol isderived from the Distributed Coordination Function (DCF) procedures byadding four independent enhanced distributed channel access functions(EDCAFs) to provide differentiated priorities to transmitted traffic,through the use of four different access categories (ACs).

Each EDCAF shall maintain a backoff timer, which has a value measured inbackoff slots. When the backoff procedure is invoked, the backoff timeris set to an integer value chosen randomly with a uniform distributiontaking values in the range [0,CW[AC]] inclusive. The duration AIFS[AC]is a duration derived from the value AIFSN[AC] by the relation:AIFS[AC]=AIFSN[AC]×aSlotTime+aSIFSTime.

In an infrastructure BSS, AIFSN[AC] is advertised by an AP in the EDCAParameter Set element in Beacon and Probe Response frames transmitted bythe AP. The value of AIFSN[AC] shall be greater than or equal to 2 fornon-AP STAs. The value of AIFSN[AC] shall be greater than or equal to 1for APs. An EDCA transmission opportunity (TXOP) which is an interval oftime during which a STA has the right to initiate frame exchangesequences onto a wireless medium is granted to an EDCAF when the EDCAFdetermines that it shall initiate the transmission of a frame exchangesequence. Transmission initiation shall be determined according to thefollowing rules:

EDCAF operations shall be performed at slot boundaries, defined asfollows on the primary channel, for each EDCAF:

a) Following AIFSN[AC]×aSlotTime−aRxTxTurnaroundTime of idle mediumafter SIFS (not necessarily idle medium during the SIFS) after the lastbusy medium on the antenna that was the result of a reception of a framewith a correct FCS.

b) Following EIFS−DIFS+AIFSN[AC]×aSlotTime+aSIFSTime−aRxTxTurnaroundTimeof idle medium after the last indicated busy medium as determined by thephysical CS mechanism that was the result of a frame reception that hasresulted in FCS error, or PHY-RXEND.indication (RXERROR) primitive wherethe value of RXERROR is not NoError.

c) When any other EDCAF at this STA transmitted a frame requiringacknowledgment, the earlier of 1) the end of the AckTimeout intervaltimed from the PHY-TXEND.confirm primitive, followed byAIFSN[AC]×aSlotTime+aSIFSTime−aRxTxTurnaroundTime of idle medium, and 2)the end of the first AIFSN[AC]×aSlotTime−aRxTxTurnaroundTime of idlemedium after SIFS (not necessarily medium idle during the SIFS, thestart of the SIFS implied by the length in the PHY header of theprevious frame) when a PHY-RXEND.indication primitive occurs.

d) Following AIFSN[AC]×aSlotTime−aRxTxTurnaroundTime of idle mediumafter SIFS (not necessarily medium idle during the SIFS) after the lastbusy medium on the antenna that was the result of a transmission of aframe for any EDCAF and which did not require an acknowledgment.

e) Following AIFSN[AC]×aSlotTime+aSIFSTime−aRxTxTurnaroundTime of idlemedium after the last indicated idle medium as indicated by the CSmechanism that is not covered by a) to d).

Following aSlotTime of idle medium, which occurs immediately after anyof these conditions, a) to f), is met for the EDCAF.

On these specific slot boundaries each EDCAF shall make a determinationto perform one and only one of the following functions: Decrement thebackoff timer, Initiate the transmission of a frame exchange sequence,Invoke the backoff procedure due to an internal collision and Donothing.

At each of the above-described specific slot boundaries, each EDCAFshall decrement the backoff timer if the backoff timer for that EDCAFhas a nonzero value.

At each of the above-described specific slot boundaries, each EDCAFshall initiate a transmission sequence if there is a frame available fortransmission at that EDCAF, and the backoff timer for that EDCAF has avalue of 0, and initiation of a transmission sequence is not allowed tocommence at this time for an EDCAF of higher UP.

At each of the above-described specific slot boundaries, each EDCAFshall report an internal collision if there is a frame available fortransmission at that EDCAF, and the backoff timer for that EDCAF has avalue of 0, and initiation of a transmission sequence is allowed tocommence at this time for an EDCAF of higher UP.

Each EDCAF shall maintain a state variable CW[AC], which shall beinitialized to the value of the parameter CWmin[AC], for that EDCAF'sAC.

Transmission failure of an MPDU is defined as follows:

-   -   After transmitting an MPDU (even if it is carried in an A-MPDU        or as part of a VHT MU PPDU that is sent using TXVECTOR        parameter NUM_USERS>1) that requires one or more immediate        response:    -   The STA shall wait for a timeout interval of duration        aSIFSTime+aSlotTime+aRxPHYStart-Delay, starting when the MAC        receives a PHY-TXEND.confirm primitive. If a        PHY-RXSTART.indication primitive does not occur during the        timeout interval, the transmission of the MPDU has failed.    -   If a PHY-RXSTART.indication primitive does occur during the        timeout interval, the STA shall wait for the corresponding        PHY-RXEND.indication primitive to recognize one or more valid        response MPDUs that either does not have a TA field or is sent        by one or more recipients of the MPDU requiring a response. If        anything else, including any other valid frame, is recognized,        the transmission of the MPDU has failed.    -   The nonfinal (re)transmission of an MPDU that is delivered using        the GCR unsolicited retry retransmission policy is defined to be        a failure.    -   In all other cases, the transmission of the MPDU has not failed.

The backoff procedure shall be invoked by an EDCAF when any of thefollowing events occurs:

a) An MA-UNITDATA.request primitive is received that causes a frame withthat AC to be queued for transmission such that one of the transmitqueues associated with that AC has now become nonempty and any othertransmit queues associated with that AC are empty; the medium is busy onthe primary channel as indicated by any of the following:

-   -   physical CS;    -   virtual CS;    -   a non-zero TXNAV timer value;

b) The transmission of the MPDU in the final PPDU transmitted by theTXOP holder during the TXOP for that AC has completed and the TXNAVtimer has expired, and the AC was a primary AC.

c) The transmission of an MPDU in the initial PPDU of a TXOP fails andthe AC was a primary AC.

d) The transmission attempt collides internally with another EDCAF of anAC that has higher priority, that is, two or more EDCAFs in the same STAare granted a TXOP at the same time.

e) The transmission attempt of a STA coordinated by an MM-SME collidesinternally with another STA coordinated by the same MM-SME, which isindicated to the first MAC entity with a PHY-TXBUSY.indication(BUSY)primitive as response to the PHY-TXS TART. request primitive.

In addition, the backoff procedure may be invoked by an EDCAF when thetransmission by the TXOP holder of an MPDU in a noninitial PPDU of aTXOP fails.

If the backoff procedure is invoked for reason a) above, the value ofCW[AC] shall be left unchanged. If the backoff procedure is invoked forreason b) above, the value of CW[AC] shall be reset to CWmin[AC].

If the backoff procedure is invoked for reason c), d), e) or f) above,or the transmission failure of a non-initial frame by the TXOP holder],the value of CW[AC] shall be updated as follows before invoking thebackoff procedure:

-   -   If the QSRC[AC] or the QLRC[AC] has reached dotl1ShortRetryLimit        or dotl1LongRetryLimit respectively, CW[AC] shall be reset to        CWmin[AC].    -   If dotl11RobustAVStreamingImplemented is true and either the        QSDRC[AC] or the QLDRC[AC] has reached dot11ShortDEIRetryLimit        or dot11LongDEIRetryLimit, respectively, CW[AC] shall be reset        to CWmin[AC].    -   Otherwise,    -   If CW[AC] is less than CWmax[AC], CW[AC] shall be set to the        value (CW[AC]+1)×2−1.    -   If CW[AC] is equal to CWmax[AC], CW[AC] shall be left unchanged.    -   For an HE STA, if CW[AC] is less than CWmin [AC], CW[AC] shall        be set to CWmin [AC].    -   For an HE STA, if CW[AC] is greater than CWmax[AC], CW[AC] shall        be set to CWmax[AC].

Regarding the CW[AC] update, the last two sub-bullets on the above rulesare happened when the EDCA parameter set is changed.

-   -   For an HE STA, if CW[AC] is less than CWmin [AC], CW[AC] shall        be set to CWmin [AC].    -   For an HE STA, if CW[AC] is greater than CWmax[AC], CW[AC] shall        be set to CWmax[AC].

Physical and virtual Carrier sense (CS) functions are used to determinethe state of the wireless medium. When either function indicates a busymedium, the medium shall be considered busy; otherwise, it shall beconsidered idle.

A physical CS mechanism shall be provided by the physical layer (PHY). Avirtual CS mechanism shall be provided by the Medium Access Control(MAC) layer. This mechanism is referred to as the network allocationvector (NAV). The NAV maintains a prediction of future traffic on themedium based on duration information that is announced inRequest-to-Send (RTS)/Clear-to-Send (CTS) frames prior to the actualexchange of data. The duration information is also available in the MACheaders of all frames sent during the contention period other thanPS-Poll frames.

The CS mechanism combines the NAV state and the STA's transmitter statuswith physical CS to determine the busy/idle state of the medium. The NAVmay be thought of as a counter, which counts down to 0 at a uniformrate. When the counter is 0, the virtual CS indication is that themedium is idle; when the counter is nonzero, the indication is busy. Themedium shall be determined to be busy when the STA is transmitting.

A STA that receives at least one valid frame in a Physical layer ServiceData Unit (PSDU) can update its NAV with the information from any validDuration field in the PSDU. When the received frame's receiver address(RA) is equal to the STA's own MAC address, the STA shall not update itsNAV. For all other received frames the STA shall update its NAV when thereceived Duration is greater than the STA's current NAV value. Uponreceipt of a PS-Poll frame, a STA shall update its NAV settings asappropriate under the data rate selection rules using a duration valueequal to the time, in microseconds, required to transmit one Ack frameplus one SIFS, but only when the new NAV value is greater than thecurrent NAV value. If the calculated duration includes a fractionalmicrosecond, that value is rounded up to the next higher integer.Various additional conditions may set or reset the NAV. When the NAV isreset, a PHY-CCARESET.request primitive shall be issued. This NAV updateoperation is performed when the PHY-RXEND.indication primitive isreceived.

The PHY-RXSTART.indication primitive is an indication by the PHY to thelocal MAC entity that the PHY has received a valid start of a PPDU,including a valid PHY header. This primitive is not generated until thePHY has determined the PPDU format. The RXVECTOR of thePHY-RXSTART.indication represents a list of parameters that the PHYprovides the local MAC entity upon receipt of a valid PHY header.

After generating a PHY-RXSTART.indication primitive, the PHY is expectedto maintain physical medium busy status (not generating aPHY-CCA.indication (IDLE) primitive) during the period required by thatPHY to transfer a frame of the indicated LENGTH at the indicatedDATARATE. This physical medium busy condition should be maintained evenif a PHY-RXEND.indication (CarrierLost) primitive or aPHY-RXEND.indication(FormatViolation) primitive is generated by the PHYprior to the end of this period.

The PHY-RXEND.indication primitive is an indication by the PHY to thelocal MAC entity that the PSDU currently being received is complete. ThePHY-RXEND.indication primitive has two parameters: RXERROR and RXVECTOR.

The RXERROR parameter of the PHY-RXEND.indication primitive can conveyNoError or one or more values indicating an error condition. A number oferror conditions may occur after the PHY's receive state machine hasdetected what appears to be a valid preamble and SFD. The followingdescribes the parameter returned for each of those error conditions.

-   -   NoError: This value is used to indicate that no error occurred        during the receive process in the PHY.    -   FormatViolation: This value is used to indicate that the format        of the received PPDU was in error.    -   CarrierLost: This value is used to indicate that during the        reception of the incoming PSDU, the carrier was lost and no        further processing of the PSDU can be accomplished.    -   UnsupportedRate: This value is used to indicate that during the        reception of the incoming PPDU, a nonsupported date rate was        detected.    -   Filtered: This value is used to indicate that during the        reception of the PPDU, the PPDU was filtered out due to a        condition set in the PHYCONFIG_VECTOR.

The RXVECTOR of the PHY-RXEND.indication primitive represents a list ofparameters that the PHY provides the local MAC entity upon receipt of avalid PHY header or upon receipt of the last PSDU data bit in thereceived frame. RXVECTOR is an included parameter only whendot11RadioMeasurementActivated is true. This vector may contain both MACand MAC management parameters.

The PHY-RXEND.indication primitive is generated by the PHY for the localMAC entity to indicate that the receive state machine has completed areception with or without errors. When a Signal Extension is present,the primitive is generated at the end of the Signal Extension. In thecase of an RXERROR value of NoError, the MAC uses thePHY-RXEND.indication primitive as reference for channel access timing.The effect of receipt of this primitive is for the MAC to begininter-frame space processing.

FIG. 1 shows various formats for HE PPDU.

HE single user (SU) PPDU, HE trigger-based (TB) PPDU and HE extendedrange (ER) SU PPDU format are destined for a single STA. HE multi-user(MU) PPDU and HE ER MU PPDU are destined for the plurality of STAs.

HE PPDU may include Non-HT Short Training field (L-STF), Non-HT LongTraining field (L-LTF), Non-HT SIGNAL field (L-SIG), Repeated Non-HTSIGNAL field (RL-SIG), HE Signal A field (HE-SIG-A), HE Signal B field(HE-SIG-A), HE Short Training field (HE STF), HE Long Training field (HELTF) and a Data field. The Data field may include a Physical layerservice data unit (PSDU).

The L-SIG is used to communicate rate and length information. The L-SIGmay include a LENGTH field and a RATE field. The RATE field may be setto the value representing 6 Mb/s in the 20 MHz channel. The LENGTH fieldmay be set to the value given by the following equation:

$\begin{matrix}{{LENGTH} = {{\left\lceil \frac{{TXTIME} - {SignalExtension} - 20}{4} \right\rceil \cdot 3} - 3 - m}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where TXTIME is described later and m is 1 for HE MU PPDU and HE ER SUPPDU, and m is 2 otherwise. SignalExtension may be a time to set NAVcorrectly and may be 0-10 μs. For example, SignalExtension may be 0 μsor 6 μs. SignalExtension may be 0 μs when TXVECTOR parameter NO_SIG_EXTNis true and aSignalExtension when TXVECTOR parameter NO_SIG_EXTN isfalse. aSignalExtension may be 0 μs when operating in the 5 GHz band 6μs when operating in the 2.4 GHz band.

The HE-SIG-A may include at least one of following fields. The number ofbits is exemplary purpose only.

TABLE 1 Number Field of bits Description UL/DL 1 Indicates whether thePPDU is sent UL or DL: i.e. Set to 0 for DL, Set to 1 for UL Format 1Differentiate an HE SU PPDU from an HE TB PPDU: i.e. Set to 0 for HE TBPPDU, Set to 1 for HE SU PPDU BSS Color 6 The BSS Color field is anidentifier of the BSS Bandwidth 2 Bandwidth over which this PPDU istransmitted. Modulation Indicated a MCS of the Data Field and CodingScheme (MCS) TXOP Indicates the remaining duration of the TXOP after theDuration transmission. Set to a value to indicate duration informationfor NAV setting and protection of the TXOP. Spatial Reuse Indicateswhether or not spatial reuse is allowed during the transmission of thisPPDU, and if allowed, indicates a value that is used to determine alimit on the transmit power of a spatial reuse transmission.

Table 2 shows timing related constants of HE PPDU

TABLE 2 Parameter Values Description T_(SYM) 13.6 μs, 14.4 μs or 14.4 μsSymbol interval depending on the GI used T_(L-STF) 8 μs Non-HT ShortTraining field duration T_(L-LTF) 8 μs Non-HT Long Training fieldduration T_(L-SIG) 4 μs Non-HT SIGNAL field duration T_(RL-SIG) 4 μsRepeated non-HT SIGNAL field duration T_(HE-SIG-A) 8 μs HE Signal Afield duration in normal mode T_(HE-SIG-A-R) 8 μs HE Signal A fieldduration in repetition/low rate mode T_(HE-STF-T) 8 μs = 5 × 1.6 μs HEShort Training field duration for trigger- based PPDU T_(HE-STF-NT) 4 μs= 5 × 0.8 μs HE Short Training field duration for non-trigger- basedPPDU T_(HE-LTF) T_(HE-LTF-1X), T_(HE-LTF-2X) or Duration of each HE-LTFsymbol without GI T_(HE-LTF-4X) depending upon the LTF duration usedT_(HE-LTF-1X) 3.2 μs Duration of each 1x HE-LTF symbol without GIT_(HE-LTF-2X) 6.4 μs Duration of each 2x HE-LTF symbol without GIT_(HE-LTF-4X) 12.8 μs Duration of each 4x HE-LTF symbol without GIT_(HE-SIG-B) 4 μs = 3.2 μs + T_(GI, Pre-HE) Duration of each HE-SIG-Bsymbol T_(PE) 0, 4 μs, 8 μs, 12 μs, 16 μs Duration of Packet Extensionfield depending on actual extension duration used N_(service) 16 Numberof bits in the SERVICE field N_(tail) 6 Number of tail bits per BCCencoder

The value of the TXTIME parameter may be calculated for an HE PPDU usingthe following:

TXTIME=20+T _(HE-PREAMBLE) +N _(SYM) T _(SYM) +T _(PE)+SignalExtension  [Equation 3]

whereT_(HE-PREAMBLE)=T_(RL-SIG)+T_(HE-SIG-A)+T_(HE-STF-T)+N_(HE-LTF)T_(HE-LTF,SYM)for HE TB PPDU,T_(HE-PREAMBLE)=T_(RL-SIG)+T_(HE-SIG-A)+T_(HE-STF-NT)+N_(HE-LTF THE-LTF,SYM)for HE SU PPDU,T_(HE-PREAMBLE)=T_(RL-SIG)+T_(HE-SIG-A)+N_(HE-SIG-B)+T_(HE-SIG-B)+T_(HE-STF-NT)+N_(HE-LTF)T_(HE-LTF,SYM) for HE MU PPDU,T_(HE-PREAMBLE)=T_(RL-SIG)+T_(HE-SIG-A)+T_(HE-SIG-A-R)+T_(HE-STF-NT)+N_(HE-LTF)T_(HE-LTF,SYM) for HE ER SU PPDU, N_(HE-LTF) is the number of OFDMsymbols in the HE-LTF field, T_(SYM)=4 μs,

${N_{SYM} = {\left\lfloor {\left( {{\frac{{LEGNTH} + m + 3}{3} \times 4} - T_{{HE}\text{-}{PREAMBLE}}} \right)/T_{SYM}} \right\rfloor - b_{{PE}\text{-}{Disambiguity}}}},{and}$$T_{PE} = {\left\lfloor {\left\{ {\left( {{\frac{{LENGTH} + m + 3}{3} \times 4} - T_{{HE}\text{-}{PREAMBLE}}} \right) - {N_{SYM}T_{SYM}}} \right\}/4} \right\rfloor \times 4.}$

b_(PE-Disambiguity) is the value indicated by a sub-field of theHE-SIG-A field. Especially, bPE-Disambiguity is derived from the PacketExtension subfield of the Common Info field in a Trigger frame when thetransmitted PPDU is an HE TB PPDU.

The value of the RXTIME may be calculated for an HE PPDU using thefollowing:

RXTIME=20+T _(HE-PREAMBLE) +N _(SYM) T _(SYM) +T _(PE)+SignalExtension  [Equation 3]

FIG. 2 shows a boundary of a PPDU.

TXTIME and RXTIME of HE PPDU represents the actual used time for atransmission and a reception. So, as shown the below figure, TXTIME andRXTIME of HE PPDU is not aligned with 4 μs boundary.

FIG. 3 shows the difference of RXTIME between HE STA and legacy STA.

When a legacy STA (such as, non-HT STA, HT STA and VHT STA) receives HEPPDU, the RXTIME is calculated as the following, based on the LENGTHsubfield of L-SIG field of the HE PPDU.

$\begin{matrix}{{RXTIME} = {{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

A protection mechanism of a HE STA is that this NAV update operation isperformed when the PHY-RXEND.indication primitive is received, exceptwhen the PHY-RXEND.indication primitive is received before the end ofthe PPDU, in this case, this NAV update operation is performed at theexpected end of the PPDU. The expected end of the PPDU is calculated byEquation 3 when the received PPDU is an HE SU PPDU, HE extended range SUPPDU or HE MU PPDU. The expected end of the PPDU is calculated as theEquation 4 when the received PPDU is HE TB PPDU.

For indicating the expected end of the PPDU for updating the NAV, aPHY-TXOP. indication primitive is defined. The PHY-TXOP.indicationprimitive is an indication by the PHY to the local MAC entity of theremaining TXOP duration after a reception. The PHY-TXOP.indicationprimitive provides TXOP_DURATION. The TXOP_DURATION parameter is set toa value indicated in the TXOP Duration field of HE-SIG-A from thereceived HE PPDU.

In TXVECTOR, TXOP_DURATION indicates a duration of time that is used toupdate the NAV for this TXOP, except for a value of 127 (i.e., all 1 s)which indicates an invalid value of TXOP duration in the HE-SIG-A field.In RXVECTOR, TXOP_DURATION indicates the remaining duration of the TXOPafter the reception. TXOP_DURATION may has B0-B6 bits. B0 indicateswhether the granularity is 8 μs or 128 μs. When B0 is 0, then B1 to B6indicate a duration, in units of 8 μs, starting from 0 to 504 us (i.e,duration=(8 μs×value of (B1-B6)) μs). When B0 is 1, then B1 to B6indicate a duration, in units of 128 μs, starting from 512 μs until 8448μs (i.e, duration=(512+128×value of (B1-B6)) μs).

FIG. 4 shows the NAV procedure of HE STA after receiving HE PPDU.

In STA 2, because PHY-RXEND.indication primitive and PHY-TXOP.indicationprimitive are occurred at the end of the PSDU, the NAV is set to eitherTXOP Duration value indicated in HE-SIG-A or Duration value indicated inMAC header.

In a case of STA 3, after decoding HE-SIG-A, it knows that the receivedPPDU is destined to OBSS STA. So, it discards the remaining PSDU. Inconsequence, PHY-RXEND.indication primitive is occurred after HE-SIG-Afor a power saving purpose. But, for a protection mechanism,PHY-TXOP.indication primitive is occurred at the end of the RXTIME. TheNAV of STA 3 is set to TXOP Duration value obtained fromPHY-TXOP.indication primitive.

In STA 4, after decoding HE-SIG-A, it knows that the received PPDU isdestined to OBSS STA. But, because the received signal strength is lessthan OBSS Packet Detection (OBSS PD) Threshold, it ignores the NAVupdate and resumes its backoff procedure. PHY-TXOP.indication primitiveis not occurred or is occurred with RXVECTOR parameter TXOP DURATION setto 0.

FIG. 5 shows an example of uplink multi-user operation.

The UL MU operation allows an AP to solicit simultaneous immediateresponse frames from one or more non-AP STAs. Non-AP STAs transmit theirresponse frames using HE TB PPDU, in either UL OFDMA, UL MU-MIMO, orboth.

An AP transmits a Trigger frame to a plurality of recipient STAs. TheTrigger frame requests a transmission of HE TB PPDU. The Trigger framesolicits and allocates resources for UL MU transmissions a SIFS afterthe PPDU that carries the Trigger frame. The Trigger frame may includeone or more User Info fields addressed to the recipient STAs. The interframe space between a PPDU that contains a Trigger frame and the HE TBPPDU is SIFS. If a Trigger frame is aggregated with other frames in anAggregated-MAC Protocol Data Unit (A-MPDU), the Trigger frame shall bethe first frame in the A-MPDU.

An AP does not set any subfields of the Common Info field to a valuethat is not supported by all the recipient STAs of the Trigger frame. AnAP shall not set any subfields of a User Info field to a value that isnot supported by the recipient STAs of the User Info field.

A recipient STA may commence the transmission of an HE TB PPDU at theSIFS time boundary after the end of a received PPDU, when the receivedPPDU contains a Trigger frame with a User Info field addressed to therecipient STA. The User Info field is addressed to a STA if the UserIdentifier subfield is equal to the association identifier (AID) of theSTA and the STA is associated with the AP.

After receiving a plurality of HE TB PPDUs from the plurality of STAs,the AP may transmits a block acknowledgement (BA) frame foracknowledging the plurality of HE TB PPDUs to the plurality of recipientSTAs.

FIG. 6 shows a format of Trigger frame.

A Duration field 111 is set to the remaining duration of the TXOP. TheDuration field 111 may be set to the estimated time required to transmitthe solicited HE TB PPDU, plus the estimated time required to transmitthe acknowledgement for the solicited HE TB PPDU, plus applicable SIFSs.

A receiver address (RA) field 112 is the address of the recipient STA. Atransmitter address (TA) field 113 is the address of the STAtransmitting the Trigger frame. A Padding field 116 extends the framelength to give the recipient STAs more time to prepare a response.

A Common Info field 114 may include at least one of following subfieldsin the Table 3. The number of bits is exemplary purpose only.

TABLE 3 Subfields Bits Description Trigger Type 4 indicates the type ofthe Trigger frame. Length 12 indicates the value of the L-SIG Lengthfield of the HE TB PPDU that is the response to the Trigger frame CSrequired 1 Set to 1 to indicate that the STAs identified in the UserInfo fields are required to sense the medium and to consider the mediumstate and the NAV in determining whether or not to respond. The CSRequired subfield is set to 0 to indicate that the STAs identified inthe User Info fields are not required to consider the medium state orthe NAV in determining whether or not to respond. Bandwidth 2 indicatesthe bandwidth in the HE-SIG-A of the HE TB PPDU. E.g. 20 MHz, 40 MHz, 80MHz, 80 + 80 MHz or 160 MHz GI And LTF 2 indicates the GI and HE-LTFtype of the HE TB PPDU Type response.

The Trigger Type subfield indicates the type of the Trigger frame. TheTrigger Type subfield encoding is defined in the below.

TABLE 4 Trigger Type field value Description 0 Basic Trigger 1Beamforming Report Poll Trigger 2 MU-BAR 3 MU-RTS 4-15 Reserved

The Trigger frame may include one or more User Info fields 115 addressedto the recipient STAs. For recipient STAs that are associated with theAP, the User Info field is addressed to a recipient STA if the value ofthe User Identifier subfield of the User Info field is equal to the AIDof the STA.

The User Info field 115 may include at least one of following subfieldsin the Table 5.

TABLE 5 Subfields Bits Description AID 12 indicates the AID of the STAallocated the resource unit (RU) to transmit the MPDU(s) in the HE TBPPDU, except for an AID equal to 0 which identifies a wildcard RU forrandom access. RU allocation 8 indicates the RU used by the HE TB PPDUof the STA identified by the User Identifier subfield. Coding Typeindicates the code type of the HE TB PPDU response of the STA identifiedby the User Identifier subfield. MCS indicates the MCS of the HE TB PPDUresponse of the STA identified by the User Identifier subfield. DCMindicates dual carrier modulation of the HE TB PPDU response of the STAidentified by the User Identifier subfield. Spatial Stream indicates thespatial streams of the HE TB PPDU response allocation of the STAidentified by User Identifier field.

FIG. 7 shows a protection when HE TB PPDU is transmitted.

The Length subfield of the Common Info field in the Trigger frameindicates the value of the L-SIG Length field of the HE TB PPDU that isthe response to the Trigger frame. The Length subfield may be set to apositive value that satisfies the following constraints:

LENGTH  mod3 = 1  and${{{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension} - {TXTIME}} < {4\mspace{14mu} {\mu s}}},$

where TXTIME is an actual transmission time of an HE TB PPDU that isdefined in Equation 2. If the Length subfield does not satisfy the aboveconstraints, the 3rd party STA can be over-protected for at most 16 μsas shown in FIG. 7.

The CS Required subfield of the Trigger frame is set to 1 to indicatethat the STAs identified in the User Info fields are required to use EDto sense the medium and to consider the medium state and the NAV indetermining whether or not to respond. The CS Required subfield is setto 0 to indicate that the STAs identified in the User Info fields arenot required to consider the medium state or the NAV in determiningwhether or not to respond. The ED-based CCA and virtual CS functions areused to determine the state of the medium if CS is required beforeresponding to a received Trigger frame.

A NAV is considered in virtual CS for a STA that is solicited by aTrigger frame for transmission unless one of the following conditions ismet:

-   -   The response generated by the STA contains an Ack frame or a        BlockAck frame and the Length subfield in the Common Info field        of the Trigger frame is less than or equal to 418    -   The NAV was set by an intra-BSS frame

If one or both of the NAVs are considered and the considered NAV'scounter is nonzero, then the virtual CS indicates busy. Otherwise, thevirtual CS is idle.

If the CS Required subfield in a Trigger frame is set to 1, the STAshall consider the status of the CCA and the virtual carrier sense (NAV)before UL MU transmission in response to the Trigger frame. In thiscase, the STA shall sense the medium using energy-detect (ED) afterreceiving the PPDU that contains the Trigger frame (i.e. during the SIFStime), and it shall perform the ED at least in the subchannel thatcontains the STA's UL allocation, where the sensed subchannel consistsof either a single 20 MHz channel or multiple of 20 MHz channels. TheSTA may transmit an HE TB PPDU when the 20 MHz channels containing theallocated RUs in the Trigger frame are considered idle; if the STAdetects that the 20 MHz channels containing the allocated RUs are notall idle, then the STA shall not transmit anything in the allocated RUs.

If the CS Required subfield in a Trigger frame is set to 0 or an UL MUresponse scheduling A-Control field is included in the received (A-)MPDUthat solicits a response, the STA may respond with an HE TB PPDU withoutregard to the busy/idle state of the medium.

The AP may set the CS Required subfield to 1 except when the AP solicitsan Ack or BlockAck frame from all scheduled HE TB PPDUs and the Lengthsubfield in the Common Info field of the Trigger frame is less than orequal to 418.

If the STA receives a Trigger frame having the CS Required subfield setto 0 but it does not receive any other frame soliciting an Ack frame ora BlockAck frame, the STA does not respond with an HE TB PPDU.

FIG. 8 shows an example of MU UL transmission.

An AP transmits a HE MU PPDU for STA1, STA2, STA3 and STA4. A triggerframe contained in the HE MU PPDU has the CS Required subfield set to 0.The STA1, STA2 and STA3 receive both the Trigger frame having the CSRequired subfield set to 0 and any other frame (i.e., QoS DATA framewith Ack Policy set to MU ACK) soliciting an Ack frame or a BlockAckframe. So, the STA1, STA2 and STA3 respond with an HE trigger-based PPDUthat carries Block ACK frame. However, the STA4 receives a Trigger framehaving the CS Required subfield set to 0 but it does not receive anyother frame soliciting an Ack frame or a BlockAck frame. In such case,the STA4 does not respond with an HE trigger-based PPDU.

However, if the STA received a Trigger frame, it knows its allocated RUfor an HE trigger-based PPDU transmission. In such case, responding withan HE trigger-based PPDU (such as QoS Null frame) can be more helpful tofor an overall performance.

On this purpose, If the STA receives a Trigger frame having the CSRequired subfield set to 0 but it does not receive any other framesoliciting an Ack frame or a BlockAck frame, the STA may respond with anHE trigger-based PPDU (especially that carries an QoS Null fame) whenthe NAV is idle and the 20 MHz channels containing the allocated RUs inthe Trigger frame are considered idle.

FIG. 9 shows the NAV procedure of HE STA after receiving HE TB PPDU.

In STA 2, because PHY-RXEND.indication primitive and PHY-TXOP.indicationprimitive are occurred at the end of the PSDU, the NAV is set to eitherTXOP Duration value indicated in HE-SIG-A or Duration value indicated inMAC header.

In a case of STA 3, after decoding HE-SIG-A, it knows that the receivedPPDU is destined to OBSS STA. So, it discards the remaining PSDU. Inconsequence, PHY-RXEND.indication primitive is occurred after HE-SIG-Afor a power saving purpose. But, for a protection mechanism,PHY-TXOP.indication primitive is occurred at the end of the RXTIME. TheNAV of STA 3 is set to TXOP Duration value obtained fromPHY-TXOP.indication primitive.

In STA 4, after decoding HE-SIG-A, it knows that the received PPDU isdestined to OBSS STA. But, because the received signal strength is lessthan OBSS Packet Detection (OBSS PD) Threshold, it ignores the NAVupdate and resumes its backoff procedure. PHY-TXOP.indication primitiveis not occurred or is occurred with RXVECTOR parameter TXOP_DURATION setto 0.

Upon receiving the transmitted PHY preamble overlapping the primary 20MHz channel in a greater than or equal to 20 MHz BSS, the PHY measures areceive signal strength. This activity is indicated by the PHY to theMAC via a PHY-CCA. indication primitive. A PHY-CCA.indication(BUSY,channel-list) primitive is also issued as an initial indication ofreception of a signal. The channel-list parameter of thePHY-CCA.indication primitive is absent when the operating channel widthis 20 MHz. The channel-list parameter is present and includes theelement primary when the operating channel width is 40 MHz, 80 MHz, 160MHz, or 80+80 MHz.

The PHY does not issue a PHY-RXSTART.indication primitive in response toa PPDU that does not overlap the primary channel, except when the PHY atan AP receives the HE-trigger based PPDU. In such case, the PHY shallissue a PHY-RXSTART.indication primitive in response to a PPDUtransmission either at the primary or at the secondary channel.

The PHY includes the most recently measured RSSI value in thePHY-RXSTART.indication(RXVECTOR) primitive issued to the MAC.

After the PHY-CCA.indication(BUSY, channel-list) primitive is issued,the PHY entity shall begin receiving the training symbols and searchingfor the preambles for NON-HT, HT, VHT, and HE PPDUs, respectively. Ifthe constellation used in the first symbol after the first long trainingfield is QBPSK, the PHY entity shall continue to detect the receivedsignal using the receive procedure for HT-GF. Otherwise, for detectingthe HE preamble, the PHY entity shall search for L-SIG and RL-SIG inorder to set the maximum duration of the data stream. If RL-SIG isdetected, the PHY entity should check the parity bit and RATE fields inL-SIG and RL-SIG. If either the check of the parity bit is invalid orthe RATE field is not set to MCSO in NON-HT, a PHY-RXSTART.indicationprimitive is not issued. If the check of the parity bit is valid and theRATE field is set to MCSO but the LENGTH field value in L-SIG is amultiple of 3, a PHY-RXSTART.indication primitive is not issued. In bothcases, the PHY should continue to detect the received signal usingnon-HT, HT, and VHT receive procedure.

PHY Receive Procedure of HE SU PPDU

If a valid parity bit and the RATE with MCSO are indicated in L-SIG andRL-SIG and the LENGTH field value in L-SIG and RL-SIG meet the conditionthat the remainder is 1 after LENGTH divided by 3, the PHY entity shouldbegin receiving the sequence of HE-SIG-A, HE-STF, and HE-LTF for HE SUPPDU and HE trigger-based. After RL-SIG, the PHY entity shall receivetwo symbols of HE-SIG-A immediately followed by HE-STF. The PHY entityshall check CRC of HE-SIG-A. If the CRC check is valid, the PHY entityshall report TXOP, BSS Color and check Format field, and continue toreceive HE-STF. The PHY entity shall report to the MAC entity thepredicted duration of the TXOP in HE-SIG-A. The PHY entity shall checkthe BSS color in HE-SIG-A. The PHY entity shall check Format field inHE-SIG-A.

If the Format field indicates an HE SU PPDU, the PHY entity receivesHE-STF for 4 μs after HE-SIG-A.

The PHY entity maintains PHY-CCA.indication(BUSY, channel-list)primitive for the predicted duration of the transmitted PPDU, as definedby RXTIME in Equation 3, except when the HE-SIG-A indicates an invalidCRC or an invalid reserved HE-SIG-A indication. In which case, The PHYentity maintains PHY-CCA.indication(BUSY, channel-list) primitive forthe predicted duration of the transmitted PPDU, as defined by thefollowing equation based on LENGTH parameter.

$\begin{matrix}{{RXTIME} = {{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

PHY Receive Procedure of HE TB PPDU

If a valid parity bit and the RATE with MCSO are indicated in L-SIG andRL-SIG and the LENGTH field value in L-SIG and RL-SIG meet the conditionthat the remainder is 1 after LENGTH divided by 3, the PHY entity shouldbegin receiving the sequence of HE-SIG-A, HE-STF, and HE-LTF for HE SUPPDU and HE trigger-based. After RL-SIG, the PHY entity shall receivetwo symbols of HE-SIG-A immediately followed by HE-STF. The PHY entityshall check CRC of HE-SIG-A. If the CRC check is valid, the PHY entityshall report TXOP, BSS Color and check Format field, and continue toreceive HE-STF. The PHY entity shall report to the MAC entity thepredicted duration of the TXOP in HE-SIG-A. The PHY entity shall checkthe BSS color in HE-SIG-A. The PHY entity shall check Format field inHE-SIG-A.

If the Format field indicates an HE TB PPDU, the PHY entity shallreceive HE-STF for 8 μs after HE-SIG-A.

For calculating the predicted duration of the transmitted PPDU, asdefined by RXTIME in Equation 3, the HE-SIG-A field of the HE TB PPDUincludes at least one of the following subfields. The numbers of bits isexemplary purpose only.

TABLE 6 Subfields Bits Description HE-LTF symbols 3 Indicates the numberof HE-LTF symbols: Set to 0 for 1 HE-LTF symbol Set to 1 for 2 HE-LTFsymbols Set to 2 for 4 HE-LTF symbols Set to 3 for 6 HE-LTF symbols Setto 4 for 8 HE-LTF symbols Other values are reserved. GI/LTF Size 3Indicates the GI duration and HE-LTF size. Set to 0 to indicate a 1xHE-LTF and 0.8 μs GI Set to 1 to indicate a 2x HE-LTF and 0.8 μs GI Setto 2 to indicate a 2x HE-LTF and 1.6 μs GI Set to 3 to indicate a 4xHE-LTF and 0.8 μs GI when both DCM in HE-SIGA1 and STBC in HE-SIGA2 areset to 1. Neither DCM nor STBC shall be applied when both DCM inHE-SIGA1 and STBC in HE-SIGA2 are set to 1. Set to 3 to indicate a 4xHE-LTF and 3.2 μs GI otherwise. PE Disambiguity 1 Indicate PEDisambiguity

However, the HE-SIG-A field of the HE TB PPDU does not have the abovesubfields. Only AP that transmitted a trigger frame before SIFS time canknow the above subfields for the received HE TB PPDU. For solving thisproblem, the CCA indication procedure upon receiving the HE TB PPDU isproposed as follows.

Proposal 1)

The PHY entity of AP STA and non-AP STA may maintainPHY-CCA.indication(BUSY, channel-list) primitive for the predictedduration of the transmitted PPDU, as defined by the following equationbased on LENGTH parameter.

$\begin{matrix}{{RXTIME} = {{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Proposal 2)

The PHY entity of AP STA that transmitted a trigger frame before SIFStime shall maintain PHY-CCA.indication(BUSY, channel-list) primitive forthe predicted duration of the transmitted PPDU, as defined by RXTIME inEquation 3, except when the HE-SIG-A indicates an invalid CRC or aninvalid reserved HE-SIG-A indication. In which case, The PHY entityshall maintain PHY-CCA.indication(BUSY, channel-list) primitive for thepredicted duration of the transmitted PPDU, as defined by the equation6.

Proposal 3)

The PHY entity of AP STA that transmitted a trigger frame before SIFStime and LENGTH parameter of the received HE TB PPDU is equal to theLength subfield of the Common Info field in the previously transmittedTrigger frame may maintain PHY-CCA.indication(BUSY, channel-list)primitive for the predicted duration of the transmitted PPDU, as definedby RXTIME in Equation 3, except when the HE-SIG-A indicates an invalidCRC or an invalid reserved HE-SIG-A indication. In which case, The PHYentity shall maintain PHY-CCA.indication(BUSY, channel-list) primitivefor the predicted duration of the transmitted PPDU, as defined by theequation 6.

Proposal 4)

The PHY entity of AP STA that transmitted a trigger frame before SIFStime and LENGTH parameter of the received HE TB PPDU is not equal to theLength subfield of the Common Info field in the previously transmittedTrigger frame may maintain PHY-CCA.indication(BUSY, channel-list)primitive for the predicted duration of the transmitted PPDU (eventhough the HE-SIG-A indicates an valid CRC or an valid reserved HE-SIG-Aindication), as defined by the equation 6.

Proposal 5)

The PHY entity of AP STA that did not transmit a trigger frame beforeSIFS time may maintain PHY-CCA.indication(BUSY, channel-list) primitivefor the predicted duration of the transmitted PPDU (In other words, thereceived HE TB PPDU) (even though the HE-SIG-A indicates an valid CRC oran valid reserved HE-SIG-A indication), as defined by the equation 6.

Proposal 6)

The PHY entity of non-AP STA shall maintain PHY-CCA.indication(BUSY,channel-list) primitive for the predicted duration of the transmittedPPDU (In other words, the received HE TB PPDU) (even though the HE-SIG-Aindicates an valid CRC or an valid reserved HE-SIG-A indication), asdefined by the equation 6.

Proposal 7)

HE-SIG-A of HE trigger-based PPDU includes at least one subfield shownin Table 7.

TABLE 7 Subfields Bits Description HE-LTF symbols 3 Indicates the numberof HE-LTF symbols: Set to 0 for 1 HE-LTF symbol Set to 1 for 2 HE-LTFsymbols Set to 2 for 4 HE-LTF symbols Set to 3 for 6 HE-LTF symbols Setto 4 for 8 HE-LTF symbols Other values are reserved. GI/LTF Size 3Indicates the GI duration and HE-LTF size. Set to 0 to indicate a 1xHE-LTF and 0.8 μs GI Set to 1 to indicate a 2x HE-LTF and 0.8 μs GI Setto 2 to indicate a 2x HE-LTF and 1.6 μs GI Set to 3 to indicate a 4xHE-LTF and 0.8 μs GI when both DCM in HE-SIGA1 and STBC in HE-SIGA2 areset to 1. Neither DCM nor STBC shall be applied when both DCM inHE-SIGA1 and STBC in HE-SIGA2 are set to 1. Set to 3 to indicate a 4xHE-LTF and 3.2 μs GI otherwise. PE Disambiguity 1 Indicate PEDisambiguity STBC 1 In an HE MU PPDU where each RU includes no more than1 user, set to 1 to indicate all RUs are STBC encoded in the payload,set to 0 to indicate all RUs are not STBC encoded in the payload. STBCis not applied in MU-MIMO RUs. DCM 1 Indicates whether or not DCM isapplied to the Data field for the MCS indicated. Set to 1 to indicatethat DCM is applied to the Data field Set to 0 to indicate that DCM isnot applied to the Data field. DCM is only applied for MCS0, MCS1, MCS3and MCS4. DCM is only applied for 1 and 2 spatial streams. DCM is notapplied when STBC is used.

Then, the PHY entity may maintain PHY-CCA.indication(BUSY, channel-list)primitive for the predicted duration of the transmitted PPDU, as definedby RXTIME in Equation 3, except when the HE-SIG-A indicates an invalidCRC or an invalid reserved HE-SIG-A indication. In which case, The PHYentity shall maintain PHY-CCA.indication(BUSY, channel-list) primitivefor the predicted duration of the transmitted PPDU, as defined by theequation 6.

PHY Receive Procedure of HE ER SU PPDU

If a valid parity bit of L-SIG and RL-SIG is indicated and the LENGTHfield value in L-SIG and RL-SIG meet the condition that the remainder is2 after LENGTH divided by 3, the PHY entity should detect the signalconstellations in the second symbol after RL-SIG. If the constellationis QBPSK, the PHY entity shall continue receiving the sequence ofHE-SIG-A, HE-STF, and HE-LTF for HE ER SU PPDU. After RL-SIG, the PHYentity shall receive four symbols of HE-SIG-A immediately followed byHE-STF. The PHY entity shall check CRC of HE-SIG-A. If the CRC check isvalid, the PHY entity shall report TXOP, BSS Color, and continue toreceive HE-STF. The PHY entity shall report to the MAC entity thepredicted duration of the TXOP in HE-SIG-A. The PHY entity shall checkthe BSS color in HE-SIG-A. If the BSS color doesn't contain an intendedvalue, the PHY entity shall set PHY_RXSTART.indication(RXVECTOR) thenset PHY_RXEND.indication(Filtered). The PHY entity shall receive HE-STFfor 4 μs after HE-SIG-A.

The PHY entity shall maintain PHY-CCA.indication(BUSY, channel-list)primitive for the predicted duration of the transmitted PPDU, as definedby RXTIME in Equation 3, except when the HE-SIG-A indicates an invalidCRC or an invalid reserved HE-SIG-A indication. In which case, The PHYentity shall maintain PHY-CCA.indication(BUSY, channel-list) primitivefor the predicted duration of the transmitted PPDU, as defined by theequation 6.

PHY Receive Procedure of HE MU PPDU

If a valid parity bit of L-SIG and RL-SIG is indicated and the LENGTHfield value in L-SIG and RL-SIG meet the condition that the remainder is2 after LENGTH divided by 3, the PHY entity should detect the signalconstellations in the second symbol after RL-SIG. If the constellationis BPSK, the PHY entity shall continue receiving the sequence ofHE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF for HE MU PPDU. After RL-SIG, thePHY entity shall receive two symbols of HE-SIG-A immediately followed byHE-SIG-B. The PHY entity shall check CRC of HE-SIG-A. If the CRC checkis valid, the PHY entity shall report TXOP, BSS Color, and continue toreceive HE-SIG-B. The PHY entity shall report to the MAC entity thepredicted duration of the TXOP in HE-SIG-A. The PHY entity shall checkthe BSS color in HE-SIG-A. If the BSS color doesn't contain an intendedvalue, the PHY entity shall set PHY_RXSTART.indication(RXVECTOR) thenset PHY_RXEND.indication(Filtered). After HE-SIG-A, the PHY entity shallreceive HE-SIG-B for the number of symbols predicted from HE-SIG-A. Ifthe common field presents in HE-SIG-B, the PHY entity shall check theCRC of the common field. If the CRC in the common field is valid or thecommon field is not present, the PHY entity shall search for intendedSTA-ID in each user-specific subfield with a valid CRC. If no CRC isvalid or no intended STA-ID is detected, the PHY entity shall setPHY_RXSTART.indication(RXVECTOR) then setPHY_RXEND.indication(Filtered). If a complete allocation of an intendedSTA-ID is detected in block with valid CRC, the PHY entity shallcontinue receiving HE-STF for 4 μs after HE-SIG-B for the detected andintended STA.

The PHY entity shall maintain PHY-CCA.indication(BUSY, channel-list)primitive for the predicted duration of the transmitted PPDU, as definedby RXTIME in Equation 3, except when the HE-SIG-A indicates an invalidCRC or an invalid reserved HE-SIG-A indication. In which case, The PHYentity shall maintain PHY-CCA.indication(BUSY, channel-list) primitivefor the predicted duration of the transmitted PPDU, as defined by theequation 6.

TXOP DURATION

For HE SU PPDU, HE extended range SU PPDU, HE TB PPDU and HE MU PPDU,the received PSDU bits are assembled into octets, decoded, and presentto the MAC using a series of PHY-DATA.indication(DATA) primitiveexchanges. Any final bits that cannot be assembled into a complete octetare considered pad bits and discarded. After the reception of the finalbit of the last PSDU octet, and possible padding and tail bits, the PHYentity shall check whether packet extension and/or signal extension isapplied. If packet extension and/or signal extension is applied, the PHYentity shall wait until the packet extension and/or signal extensionexpires before returning to the RX IDLE state.

TXOP Duration field is carried in the TXVECTOR parameter TXOP_DURATIONof an HE PPDU and indicates duration information for NAV setting andprotection of TXOP.

A STA that transmits an HE SU PPDU, HE ER SU PPDU, or HE MU PPDU mayindicate no duration information for NAV setting by setting the TXVECTORparameter TXOP_DURATION to all 1 s.

If a STA transmits an HE SU PPDU, HE ER PPDU, or HE MU PPDU that carriesa PS-Poll frame, the STA shall set the TXVECTOR parameter TXOP_DURATIONto all 1 s.

A TXOP responder that transmits an HE TB PPDU shall set the TXVECTORparameter TXOP_DURATION to all 1 s if the RXVECTOR parameterTXOP_DURATION of the soliciting PPDU is set to all 1 s.

A TXOP responder that transmits an HE TB PPDU shall not set the TXVECTORparameter TXOP_DURATION to all 1 s if any one of the followingconditions is met:

-   -   The RXVECTOR parameter TXOP_DURATION of the soliciting PPDU is        not set to all is    -   The RXVECTOR parameter FORMAT of the soliciting PPDU is not        equal to HE_SU, HE_MU, or HE_EXT_SU

If the TXVECTOR parameter TXOP_DURATION of an HE PPDU is not set to all1 s, and there exists Duration field in the MAC header of the HE PPDU,the duration information indicated by the TXVECTOR parameterTXOP_DURATION is determined based on the duration information indicatedby the Duration field in the MAC header (see the below Equation 7 orEquation 8) and shall indicate the largest feasible duration informationthat is smaller than or equal to the duration information indicated bythe Duration field. Except for a PS-Poll frame and an HE NDP PPDU, theDuration/ID field in a data frame, management frame and control frameindicates duration information. For a TXOP responder, the Duration fieldin the MAC header of the response PPDU is set based on the Durationfield in the MAC header of the soliciting PPDU.

$\begin{matrix}{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D}{8} \right\rfloor},504} \right)},{128\left\lfloor \frac{D}{128} \right\rfloor}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

where D represents the value of the Duration field in the MAC header ofthe transmitting HE PPDU.

$\begin{matrix}{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D}{8} \right\rfloor},504} \right)},{\min \left( {{128\left\lfloor \frac{D}{128} \right\rfloor},8448} \right)}} \right\}}} & \left\lbrack {{Equation}\mspace{11mu} 8} \right\rbrack\end{matrix}$

For a TXOP responder that transmits an HE TB PPDU carrying either aPS-Poll frame or an HE NDP, if the TXOP responder does not set theTXVECTOR parameter TXOP_DURATION of the HE TB PPDU to all ls, the TXOPresponder first calculates potential duration information equal to theduration information indicated by the Duration field of the frame thatsolicits the response minus the time, in microseconds, between the endof the PPDU carrying the frame that soliciting the HE TB PPDU and theend of the HE TB PPDU.

The time, in microseconds, between the end of the PPDU carrying theframe that soliciting the HE TB PPDU and the end of the HE TB PPDUcarrying either a PS-Poll frame or an HE NDP is defined by the followingequation.

$\begin{matrix}{{SIFS} + {\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

where SIFS is 10 μs when operating in the 2.4 GHz band and is 16 μs whenoperating in the 5 GHz band. LENGTH is the value of the Length subfieldof the Common Info field in the Trigger frame in the soliciting PPDU.LENGTH may be equivalent to LENGTH parameter carried in the HE TB PPDU.

If the calculated potential duration information includes a fractionalmicrosecond, the potential duration information is rounded up to thenext higher integer. Then the duration information indicated by theTXVECTOR parameter TXOP_DURATION is determined based on the calculatedpotential duration information (see the below Equation 10 or Equation11) and shall indicate the largest feasible duration information that issmaller than or equal to the calculated potential duration information.

$\begin{matrix}{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D^{\prime}}{8} \right\rfloor},504} \right)},{128\left\lfloor \frac{D^{\prime}}{128} \right\rfloor}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

where D′ represents the calculated potential duration.

$\begin{matrix}{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D^{\prime}}{8} \right\rfloor},504} \right)},{\min \left( {{128\left\lfloor \frac{D^{\prime}}{128} \right\rfloor},8448} \right)}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

For a TXOP holder that transmits an HE NDP PPDU, if the TXOP holder doesnot set the TXVECTOR parameter TXOP_DURATION of the HE NDP PPDU to allls, the TXOP holder first calculates potential duration informationequal to the duration information indicated by the Duration field of thepreceding HE NDP Announcement frame minus the time, in microseconds,between the end of the PPDU carrying the HE NDP Announcement frame andthe end of the HE NDP PPDU.

The time, in microseconds, between the end of the PPDU carrying the HENDP Announcement frame and the end of the HE NDP PPDU is defined bySIFS+TXTIME, where TXTIME=20+T_(HE-PREAMBLE)+T_(PE)+SignalExtension.

If the calculated potential duration information includes a fractionalmicrosecond, the potential duration information is rounded up to thenext higher integer. Then the duration information indicated by theTXVECTOR parameter TXOP_DURATION is determined based on the calculatedpotential duration information (see the Equation 12 or Equation 13) andshall indicate the largest feasible duration information that is smallerthan or equal to the calculated potential duration information.

$\begin{matrix}{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D^{\prime}}{8} \right\rfloor},504} \right)},{128\left\lfloor \frac{D^{\prime}}{128} \right\rfloor}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

where D′ represents the calculated potential duration.

$\begin{matrix}{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D^{\prime}}{8} \right\rfloor},504} \right)},{\min \left( {{128\left\lfloor \frac{D^{\prime}}{128} \right\rfloor},8448} \right)}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

When the Duration field in the MAC header of the HE NDP Announcementframe is set to DN, TXOP_DURATION can be calculated as Equations 13-16.

$\begin{matrix}{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{\left\lceil {D_{N} - {SIFS} - {TXTIME}} \right\rceil}{8} \right\rfloor},504} \right)},{128\left\lfloor \frac{\left\lceil {D_{N} - {SIFS} - {TXTIME}} \right\rceil}{128} \right\rfloor}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack \\{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D_{N} - {SIFS} - \left\lfloor {TXTIME} \right\rfloor}{8} \right\rfloor},504} \right)},{128\left\lfloor \frac{D_{N} - {SIFS} - \left\lfloor {TXTIME} \right\rfloor}{128} \right\rfloor}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack \\{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{\left\lceil {D_{N} - {SIFS} - {TXTIME}} \right\rceil}{8} \right\rfloor},504} \right)},{\min \left( {{128\left\lfloor \frac{\left\lceil {D_{N} - {SIFS} - {TXTIME}} \right\rceil}{128} \right\rfloor},8448} \right)}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack \\{{TXOP\_ DURATION} = {\max \left\{ {{\min \left( {{8\left\lfloor \frac{D_{N} - {SIFS} - \left\lfloor {TXTIME} \right\rfloor}{8} \right\rfloor},504} \right)},{\min \left( {{128\left\lfloor \frac{D_{N} - {SIFS} - \left\lfloor {TXTIME} \right\rfloor}{128} \right\rfloor},8448} \right)}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

Here, TXTIME=20+T_(HE-PREAMBLE)+T_(PE)+SignalExtension.

For the HE TB PPDU, when TXOP responders calculate the Duration field inthe MAC header of the HE trigger-based PPDU, all TXOP responders shallhave an identical calculated value. If TXOP responders have differentvalues (i.e., the Duration field in the MAC header of the HE TB PPDU),the TXVECTOR parameter TXOP_DURATION values of the HE TB PPDUstransmitted from TXOP responders can also have different values. In suchcase, 3rd party STA can't decode the TXOP Duration field carried in theTXVECTOR parameter TXOP_DURATION of an HE TB PPDU.

In order to solve this problem, the following mechanism is proposed tocalculate the Duration field in the MAC header of the HE TB PPDU.

Proposal 1)

In HE SU PPDU, HE ER SU PPDU, HE TB PPDU and HE MU PPDU transmitted by aSTA (i.e., TXOP responder) that is not the TXOP holder, the Duration/IDfield is set to the value obtained from the Duration/ID field of theframe that elicited the response minus the time, in microseconds,between the end of the PPDU carrying the frame that elicited theresponse and the end of the PPDU carrying the frame. The time, inmicroseconds, between the end of the PPDU carrying the frame thatelicited the response and the end of the PPDU carrying the frame isdefined by SIFS+TXTIME, where TXTIME is defined in Equation 2.

FIG. 10 shows an example of the Duration field in the HE TB PPDU.

D1 denotes the value obtained from the Duration field in the MAC headercarried in any PPDU including Trigger frame. The Duration field in theMAC header carried in HE TB PPDU may be set to D1-(SIFS+TXTIME).

An issue of this proposal 1 is that 3rd party STA's NAV time updatedbased on the TXOP_DURATION can exceed the remaining TXOP duration.Because the NAV update timing that is occurred at PHY-RXEND.indicationprimitive is not same with the end of the HE TB PPDU transmission.

FIG. 11 shows an example of the Duration field in the HE SU PPDU, HE ERSU PPDU and HE MU PPDU.

D2 denotes the value obtained from the Duration field in the MAC headercarried in any PPDU. The Duration field in the MAC header carried in HETB PPDU may be set to D2-(SIFS+TXTIME).

In case of the HE SU PPDU, HE ER SU PPDU and HE MU PPDU, the issuehappened in the HE TB PPDU is not occurred. Because the NAV updatetiming that is occurred at PHY-RXEND.indication primitive is same withthe end of the HE SU PPDU transmission.

Proposal 2)

This proposal is to solve the issue of the proposal 1. In an HE TB PPDUtransmitted by a STA (i.e., TXOP responder) that is not the TXOP holder,the Duration/ID field is set to the value obtained from the Duration/IDfield of the frame that elicited the response minus the time, inmicroseconds, between the end of the PPDU carrying the frame thatelicited the response and the end of the PPDU carrying the frame. Thetime, in microseconds, between the end of the PPDU carrying the frame(i.e., Trigger frame) that elicited the response and the end of the PPDU(i.e., HE TB PPDU) carrying the frame is defined by the followingequation.

$\begin{matrix}{{SIFS} + {\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

where LENGTH is the value obtained from the Length subfield of theCommon Info field in the Trigger frame in the soliciting PPDU. Also,LENGTH is equivalent to LENGTH parameter carried in the HE TB PPDU.

Meanwhile, when a TXOP responder transmits other HE PPDUs (such as, HESU PPDU, HE ER SU PPDU and HE MU PPDU), it calculates the Duration fieldin the MAC header as the following.

In HE SU PPDU, HE ER SU PPDU and HE MU PPDU transmitted by a STA (i.e.,TXOP responder) that is not the TXOP holder, the Duration/ID field isset to the value obtained from the Duration/ID field of the frame thatelicited the response minus the time, in microseconds, between the endof the PPDU carrying the frame that elicited the response and the end ofthe PPDU carrying the frame. The time, in microseconds, between the endof the PPDU carrying the frame that elicited the response and the end ofthe PPDU carrying the frame is defined by SIFS+TXTIME, where TXTIME isdefined in Equation 2.

FIG. 12 shows an example of the Duration field in the HE TB PPDU.

D1 denotes the value obtained from the Duration field in the MAC headercarried in any PPDU including Trigger frame. The Duration field in theMAC header carried in HE TB PPDU is set to:

$\begin{matrix}{{D\; 1} - \left\{ {{SIFS} + {\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension}} \right\}} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack\end{matrix}$

where LENGTH is the value obtained from the Length subfield of theCommon Info field in the Trigger frame in the soliciting PPDU.

FIG. 13 shows an example of the Duration field in the HE SU PPDU, HE ERSU PPDU and HE MU PPDU.

D2 denotes the value obtained from the Duration field in the MAC headercarried in any PPDU. The Duration field in the MAC header carried in HETB PPDU is set to D2-(SIFS+TXTIME).

Virtual Carrier Sense Mechanism

An HE non-AP STA maintains two NAV timers. An HE AP STA may maintain twoNAV timers.

For the two NAVs maintained by an HE STA, one is identified as intra-BSSNAV, and the second one is identified as basic NAV. Intra-BSS NAV isused to store NAV value, if needed, from a PPDU identified as intra-BSS.Basic NAV is used to store NAV value, if needed, from a PPDU identifiedas inter-BSS or cannot be identified as intra-BSS or inter-BSS.

A frame received by the STA is an intra-BSS frame if one of thefollowing conditions is true:

-   -   The RXVECTOR parameter BSS COLOR in the received PPDU carrying        the frame is the same as the BSS color announced by the AP to        which the STA is associated    -   The RA field, TA field or BSSID field of the received frame with        the Individual/Group bit forced to the value 0 is the same as        the BSSID of AP to which the STA is associated    -   The AP to which the STA is associated is a member of a Multiple        BSSID Set with two or more members and the RA field, TA field or        BSSID field of the received frame with the Individual/Group bit        forced to the value 0 is same as the BSSID of any member of the        Multiple BSSID Set    -   The RXVECTOR parameter PARTIAL_AID in the received VHT PPDU with        the RXVECTOR parameter GROUP_ID equal to 0 is the same as the        BSSID[39:47] of the AP to which the STA is associated    -   The value of RXVECTOR parameter PARTIAL_AID [5:8] in the        received VHT PPDU with the RXVECTOR parameter GROUP_ID equal to        63 is the same as the partial BSS color announced by the AP to        which the STA is associated when the Partial BSS Color field in        the most recently received HE Operation element is 1.    -   The frame is a control frame that does not have a TA field and        the RA matches the saved TXOP holder address for the BSS to        which it is associated.

A frame received by the STA is an inter-BSS frame if one of thefollowing conditions is true:

-   -   The RXVECTOR parameter BSS_COLOR of the PPDU carrying the frame        is not 0 and does not match the BSS color announced by the HE AP        to which the STA is associated.    -   The RXVECTOR parameter BSS_COLOR of the PPDU carrying the frame        is present and the STA is associated to the legacy AP.    -   When the RXVECTOR parameter BSS_COLOR of the PPDU carrying the        frame is not present, the BSSID field of the received frame with        Individual/Group bit forced to the value 0, if available, does        not match the BSSID of AP to which the STA is associated or if        the BSSID field is not available, both the RA and TA fields        exist, and none of the address fields of the received frame with        Individual/Group bit forced to the value 0 match the BSSID of AP        to which the STA is associated    -   The AP to which the STA is associated is a member of a Multiple        BSSID Set with two or more members and the BSSID field of the        received frame with Individual/Group bit forced to the value 0,        if available, does not match the BSSID of any member of the        Multiple BSSID Set    -   If the AP to which the STA is associated is a member of a        Multiple BSSID Set with two or more members, the BSSID field is        not available, both the RA and TA fields exist, and none of the        address fields of the received frame with the Individual/Group        bit forced to the value 0 match the BSSID of any member of the        Multiple BSSID Set    -   The RXVECTOR parameter PARTIAL_AID of the received VHT PPDU        frame with the RXVECTOR parameter GROUP_ID equal to 0 is        different from the BSSID[39:479 of the AP to which the STA is        associated    -   The value of RXVECTOR parameter PARTIAL_AID [5:8] in the        received VHT PPDU with the RXVECTOR parameter GROUP_ID equal to        63 is different from the partial BSS color announced by the AP        to which the STA is associated when the Partial BSS Color field        in the most recently received HE Operation element is 1.    -   An HE AP receives either a VHT MU PPDU or an HE MU PPDU.

If the received frame satisfies both intra-BSS and inter-BSS conditions,the decision made by using the MAC address takes precedence over thedecision made by using the RXVECTOR parameter BSS_COLOR.

If the received frame does not satisfy any of the intra-BSS andinter-BSS conditions, then the frame cannot be determined as intra-BSSor inter-BSS frame.

For an HE STA maintaining two NAVs (i.e., intra-BSS NAV and basic NAV),if both the NAV timers are 0, the virtual CS indication is that themedium is idle; if one of the two NAV timers is nonzero, the virtual CSindication is that the medium is busy except for a TXOP responder. TheTXOP responder considers only the basic NAV for the virtual CSindication. For example, when the TXOP responder receives a RTS frame ora Trigger frame, the virtual CS indication that is considered in the CTSand HE trigger-based PPDU response is that the medium is idle if thebasic NAV is 0 regardless of an intra-BSS NAV.

FIG. 14 shows a block diagram of a device to implement embodiments ofthe present invention.

A device may include a processor 21, a memory 22, and a transceiver 23.The processor 21 implements an operation of the STA according to theembodiment of the present invention. The processor 21 may generate aPPDU according to an embodiment of the present invention and mayinstruct the transceiver 23 to transmit the PPDU. The memory 22 storesinstructions for the operation of the processor 21. The storedinstructions may be executed by the processor 21 and may be implementedto perform the aforementioned operation of the STA. The transceiver 23transmits and receives a radio signal.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The transceiver may include a baseband circuit for processing a radiosignal. When the above-described embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memory and executed by the processor. The memory may be disposed tothe processor internally or externally and connected to the processorusing a variety of well-known means.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method for transmitting a physical layerprotocol data unit (PPDU) in a wireless local area network, the methodbeing performed by an access point (AP), the method comprising:transmitting a trigger frame for requesting a transmission of a responsePPDU to a station, the trigger frame including a first length field anda resource allocation field, the resource allocation field indicating aresource allocated to the transmission of the response PPDU, wherein thefirst length field in the trigger frame is set to a value given by:${LENGTH} = {{\left\lceil \frac{{TXTIME} - {SignalExtension} - 20}{4} \right\rceil \times 3} - 3 - m}$where TXTIME is a transmission time of the responsive PPDU,SignalExtension is 0 microseconds (μs) or 6 μs, and m is a valuesatisfying LENGTH mod 3=1; receiving the response PPDU as a response tothe trigger frame from the station, the response PPDU including an L-SIGfield, a repeated L-SIG field, an HE-SIG-A field, an HE-STF field and anHE-LTF field; checking a cyclic redundancy check (CRC) of the HE-SIG-Afield in the response PPDU; and if the CRC of the HE-SIG-A field isvalid and a reserved HE-SIG-A indication is not indicated, maintaining aclear channel assessment (CCA) indication as busy during a RXTIME1defined by:RXTIME1=20+T_(HE-PREAMBLE)+N_(SYM)T_(SYM)+T_(PE)+SignalExtension where:T_(HE-PREAMBLE)=T_(RL-SIG)+T_(HE-SIG-A)+T_(HE-STF-T)+N_(HE-LTF)T_(HE-LTF,SYM), T_(RL-SIG) is a duration of the repeated L-SIG field,T_(HE-SIG-A) is a duration of the HE-SIG-A field, T_(HE-STF-T) is aduration of the HE-STF field, N_(HE-LTF) is the number of orthogonalfrequency division multiplexing (OFDM) symbols in the HE-LTF field,T_(HE-LTF,SYM) is a duration of each OFDM symbol in the HE-LTF field,T_(SYM) is an OFDM symbol interval,${N_{SYM} = {\left\lfloor {\left( {{\frac{{LENGTH} + m + 3}{3} \times 4} - T_{{HE}\text{-}{PREAMBLE}}} \right)/T_{SYM}} \right\rfloor - b_{{PE}\text{-}{Disambiguity}}}},{T_{PE} = {\left\lfloor {\left\{ {\left( {{\frac{{LENGTH} + m + 3}{3} \times 4} - T_{{HE}\text{-}{PREAMBLE}}} \right) - {N_{SYM}T_{SYM}}} \right\}/4} \right\rfloor \times 4}},$and b_(PE-Disambiguity) is a value obtained from the trigger frame. 2.The method of claim 1, further comprising: if the reserved HE-SIG-Aindication is indicated, maintaining a CCA indication as busy during aRXTIME2 defined by:${{RXTIME}\; 2} = {{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {{SignalExtension}.}}$3. The method of claim 2, further comprising: if the CRC of the HE-SIG-Afield is invalid, maintaining a CCA indication as busy during theRXTIME2.
 4. The method of claim 1, wherein m is a value furthersatisfying following condition:${{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension} - {TXTIME}} < {4\mspace{14mu} {{\mu s}.}}$5. The method of claim 1, wherein the response PPDU further includes asecond length field being set to the value of LENGTH.
 6. A device fortransmitting a physical layer protocol data unit (PPDU) in a wirelesslocal area network, the device comprising: a processor; and a memoryoperatively coupled with the processor and configured to storeinstructions that, when executed by the processor, cause the device toperform functions comprising: transmitting a trigger frame forrequesting a transmission of a response PPDU to a station, the triggerframe including a first length field and a resource allocation field,the resource allocation field indicating a resource allocated to thetransmission of the response PPDU, wherein the first length field in thetrigger frame is set to a value given by:${LENGTH} = {{\left\lceil \frac{{TXTIME} - {SignalExtenion} - 20}{4} \right\rceil \times 3} - 3 - m}$where TXTIME is a transmission time of the responsive PPDU,SignalExtension is 0 microseconds (μs) or 6 μs, and m is a valuesatisfying LENGTH mod3=1; receiving the response PPDU as a response tothe trigger frame from the station, the response PPDU including an L-SIGfield, a repeated L-SIG field, an HE-SIG-A field, an HE-STF field and anHE-LTF field; checking a cyclic redundancy check (CRC) of the HE-SIG-Afield in the response PPDU; and if the CRC of the HE-SIG-A field isvalid and a reserved HE-SIG-A indication is not indicated, maintaining aclear channel assessment (CCA) indication as busy during a RXTIME1defined by: RXTIME1=20+T_(HE-PREAMBLE)+N_(SYM)T_(SYM)+T_(PE)+SignalExtension where:T_(HE-PREAMBLE)=T_(RL-SIG)+T_(HE-SIG-A)+T_(HE-STF-T)+N_(HE-LTF)T_(HE-LTF,SYM),T_(RL-SIG) is a duration of the repeated L-SIG field, T_(HE-SIG-A) is aduration of the HE-SIG-A field, T_(HE-STF-T) is a duration of the HE-STFfield, N_(HE-LTF) is the number of orthogonal frequency divisionmultiplexing (OFDM) symbols in the HE-LTF field, T_(HE-LTF,SYM) is aduration of each OFDM symbol in the HE-LTF field, T_(SYM) is an OFDMsymbol interval,${N_{SYM} = {\left\lfloor {\left( {{\frac{{LENGTH} + m + 3}{3} \times 4} - T_{{HE}\text{-}{PREAMBLE}}} \right)/T_{SYM}} \right\rfloor - b_{{PE}\text{-}{Disambiguity}}}},{T_{PE} = {\left\lfloor {\left\{ {\left( {{\frac{{LEGNTH} + m + 3}{3} \times 4} - T_{{HE}\text{-}{PREAMBLE}}} \right) - {N_{SYM}T_{SYM}}} \right\}/4} \right\rfloor \times 4}},$and b_(PE-Disambiguity) is a value obtained from the trigger frame. 7.The device of claim 6, wherein the functions further comprise: if thereserved HE-SIG-A indication is indicated, maintaining a CCA indicationas busy during a RXTIME2 defined by:${{RXTIME}\; 2} = {{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {{SignalExtension}.}}$8. The device of claim 7, wherein the functions further comprise: if theCRC of the HE-SIG-A field is invalid, maintaining a CCA indication asbusy during the RXTIME2.
 9. The device of claim 6, wherein m is a valuefurther satisfying following condition:${{\left\lceil \frac{{LENGTH} + 3}{3} \right\rceil \cdot 4} + 20 + {SignalExtension} - {TXTIME}} < {4\mspace{14mu} {{\mu s}.}}$10. The device of claim 6, wherein the response PPDU further includes asecond length field being set to the value of LENGTH.